There are major changes in sleep and wake that occur with age in all species studied. The major changes are in the ability to sustain state, in particular wakefulness, and reduced amounts of sleep. These physiological changes with age make older adults vulnerable to conditions that lead to difficulty sustaining sleep and wakefulness. This program of research investigates mechanisms for this at a fundamental molecular level. The projects focuses on two key groups of neurons: a) orexin cells in the lateral hypothalamus that stabilize behavioral state and promote wakefulness and b) galanin cells in the ventrolateral preoptic (VLPO) area that are active during sleep and promote sleep. We propose that there will first be decreased transcriptional response to neuronal activation in these neural populations with cell loss occurring at a later age. A major hypothesis being addressed is that changes in these neuronal populations with age are the result of age-related changes in the ER stress response pathway. To address these key hypotheses, we have three specific aims. In Aim 1, we will assess the temporal association between 3 measures of neuronal function of orexin cells and a key behavioral variable that is affected by age, i.e., the ability for mice to sustain long bouts of wakefulness. In Aim 2 we will have a similar approach but studying galanin VLPO cells with behavioral measures being reduction in NREM sleep across 24 hours and the amount of NREM in the first 24 hours of recovery sleep following 6 hours of sleep deprivation. Aim 3 will focus on the ER stress response pathway. Changes in expression of key genes in this pathway with age in these neuronal populations will be assessed. Moreover, we will determine, using a transgenic approach, whether reductions in the master regulator of the ER stress response pathway in BiP leads to changes with age being accelerated both in terms of function and number of cells in these neuronal groups and also in sleep/wake behavior. Finally, a discovery aim is proposed to use the new technology, RNA sequencing, to assess changes with age in the transcriptome of these two neuronal populations. RELEVANCE (See instructions): Fragmentation of sleep and wake occur with age. There is a reduction in the ability to sustain wakefulness and reductions in sleep. This has adverse consequences and reduces the quality of life. The mechanisms underiying these changes are unknown. This project takes a mechanistic approach focusing on specific brain neurons that control sleep and wake. This study will identify new molecular pathways to target to reduce this key effect of aging on an important behavior.